1. Field of the Invention
This invention relates generally to a method for calculating multi-directional composites in finite element method (FEM) simulations and, more particularly, to a method for calculating multi-directional composites in FEM simulations that includes converting complex fiber structures being simulated into simplified single layer elements and determining the stress on the elements so as to reduce the calculations required to simulate the stress on each individual fiber in the structures.
2. Discussion of the Related Art
Hydrogen is a very attractive fuel because it is clean and can be used to efficiently produce electricity in a fuel cell. The automotive industry expends significant resources in the development of hydrogen fuel cell systems as a source of power for vehicles. Such vehicles would be more efficient and generate fewer emissions than today's vehicles employing internal combustion engines.
Typically, hydrogen is stored in compressed gas tanks under high pressure on the vehicle to provide the hydrogen necessary for the fuel cell system. The pressure in the compressed tank can be upwards of 700 bar. In one known design, the compressed tank includes an inner plastic liner that provides a gas tight seal for the hydrogen, and an outer carbon fiber composite layer that provides the structural integrity of the tank. Because hydrogen is a very light and diffusive gas, the inner liner and the tank connector components, such as O-rings, must be carefully engineered in order to prevent leaks. The hydrogen is removed from the tank through a pipe. At least one pressure regulator is typically provided that reduces the pressure of the hydrogen within the tank to a pressure suitable for the fuel cell system.
The material used for the outer layer of high pressure tanks and vessels of the type used for hydrogen storage tanks is typically a composite including a combination of a fiber and matrix materials where the fibers are oriented in various directions. One fiber orientation is referred to as a ply or a layer. The stacking of different fiber orientations is referred to a layer set-up. The fibers are wound on a mandrel using a predetermined fiber winding process to form the outer layer of the vessel.
When designing a vessel of this type, a finite element method (FEM) algorithm is typically employed that simulates how the composite fibers can be wound with the different fiber orientations to satisfy the desired structural integrity of the tank. FEMs are well known structural design and analysis methods that can simulate the stresses that may occur on the tank. The algorithms use various inputs, including the composite material properties, fiber orientations, location of the vessel in the vehicle, etc. For a hydrogen storage tank for a fuel cell vehicle, it is necessary to determine the stress locations on the tank that may occur as a result of a vehicle crash. In this regard, the location of the tank is important because of the structural vehicle elements that are around the tank that may puncture the tank in a crash event. Thus, the algorithm considers stresses on the tank during the simulation to determine whether the vessel will withstand the stresses satisfactorily. However, because of the nature of the simulation and the calculations that go into determining the stresses on each fiber for the different situations, the amount of computing cost and computing time for such FEM simulations is significant.